I took the opportunity to weigh my S-Lites on some shipping scales, and was shocked at their heavy mass.

Tire and wheel combo (with performance Pirelli Runflats) was 49 lbs each.

I'm guessing that the Runflat tires themselves are highly to blame for this. Has anyone actually weighed a Runflat in this size? If the weight is primarily from the tire, I'll just change out the tires to some non-runflats.

If it's the wheel compound itself, I'll need to change the wheels.

If anyone has non-runflat tires on their S-Lites, let me know what your wheel/tire combo weighs!

 

yeah, the Pirellis are heavy, but the S-Lites are heavy as well, some 23lbs. its gross. I have the same problem, non-runflats are the way to go, the X-Lites are a mere 16lbs and wiith non runflats, a lot of weight is saved.

 

I would say the rims are at fault. I believe they weigh 25lbs each. That's a lot of butter to be hauling around in each corner!

 

My MINI brother, S-lite wheels are the main problem here!! Those things are very, very heavy!!! There is a THREAD on NAM somewhere that has the official wheight, etc., but that is why so many NAM members call S-lites, S-heavies!! The runflats, if they are the summer performance tires, are actually not that heavy, but they do not GRIP near as well as a non-runflat, and of course they ride much worse!! I switched my S-heavies out almost as soon as I got my car, and got some much lighter rims, and non-runflat tires!! A huge acceleration difference is 100% noticeable, not to mention with the new tires and less unsprung wheight/rotating mass, the car handles much better. I discovered how heavy they really were when I drove my wife's Cooper S with the stock 16" wheels,which are actually a fairly light wheel, and her car was way faster than mine. MIne felt like it had boat anchors holding it back, and after the change to lighter rims, I realized that it did! Peace, and good luck with your new wheel search!!

 

Let's not forget braking. If you get lighter wheels there will be less rotational mass to stop. That should equal better braking.

 

https://www.northamericanmotoring.co...ead.php?t=2152

 

17x7 stock S-lyte rims are 25.1 pounds each and the runflat and rim combo is usually about 48+ pounds each.

The R90 two piece rim is not light either, about 24 pounds.

Non runflats in similar size can be lighter about 21-22 pounds or heavy as in the case of Bridgestone Potenza S-03s but they do perform better and ride quality is better than with runflats.

If you think that heavy wheels hurt the MCS just try putting the S-lytes with runflats on the MC.

 

Does anyone have any actual performance figures for the difference, 0-60?

 

I did just that on my last car, and the difference was not that dramatic, actually. I'm sure they probably hurt me by a couple of tenths 0-60, but that is on top of more than 8 secs already. Maybe this is something you can feel at the limit on the track, but was nearly imperceptible to me on the street. Biggest difference was in "tram lining" - the 17' S-lites/runflats were much worse than my 16" R83s/runflats.

 

I was using s-lites with dunlop runflats for several weeks recently and then I put the SSRs back on and I felt the difference immediately in acceleration. It's minor but a tenth here or there begins to add up.

 

I compared the 17" S-Lite with Run Flat (49lbs) vs. my 14lb Enkei RPO-1 with Azenis (34lbs) a few years ago:
The lighter was .3 seconds consistently faster 0-60.
The lighter broke 15 feet faster from 60-0.
Search MINI2.com for the original stuff if you want.

Brian

 

I found your post. I don't agree that it shows anything concrete.

'Here's the results:

17's
-----
0-60mph = 7.37, 6.74, 6.85 seconds
60-0mph = 127, 125, 133 feet

16's
-----
0-60mph = 6.57, 6.67, 6.52 seconds
60-0mph = 115, 111, 113 feet

Again, take these numbers for what they are, a comparison via a G-Tech.'


First, a G-Tech is not as accurate as a track timer, or a radar gun.

Second, I notice the quotes regarding this test always refered to the biggest time difference. Well if I choose to go the other route, the difference was a whopping 0.07 seconds. A far cry from the 0.4 thrown around. Either way, this does not add up to the theoretical 400 lbs. difference either.

Third, either the driving or the measurement needs to be MUCH more consistent for any kind of valuable comparison. These times are far too spread, even on the same equipment runs. I'm not saying you did anything wrong, I'm just saying that basing conclusions from inconsistent numbers isn't a good idea.

I'm sure going to lighter wheels/tires has some effect. What I'm not sure about is if the amount of that effect is anything noticeable on the street. I know that many times after a mod, people's butt-dynos like to feel what they want to feel.

It would be good if there was some kind of professional test of wheel/tire weight - I'm sure it's been done by some mag sometime...

 

The only accurate test would be with a machine on your brake pedal to press at the same rate, pressure, and TIMING each run. At 60 mph trying to hit the brakes at the exact millisecond you cross a given point is nearly impossible to duplicate. I agree, the testing is not real accurate. I don't know how Car and Driver or other testers can claim accurate braking distance in feet. And having the brakes heated after each pass may even affect braking distance. You'd have to let the car cool each time you did the test, and make sure the road surface was the identical temp and location.

But obvious physics dictate that the car will brake quicker, have better acceleration, and have less unsprung weight for a better ride and handling characteristics. With that in mind, I would certainly expect to see SOME kind of improvement from real world and the G-tech.

 

The motor can only extract so many joules (unit of energy) per revolution. That energy does work to accelerate the car, and spin rotating parts. If you drop 30 lbs, that's a bit better than a 1% drop in total weight. Faster 0-60 times are assured, for a 7 second 0-60, that's almost a tenth. And this ignores the rotational mass as well. So a total improvement of 2-3 tenths is a pretty good estimate.

At 60 mph, you're moving 88 feet per second. So you hit 60 about 20 feet earlier. If you do stop-light racing, you know how far that is.

To get accurate breaking distances, you don't measure from the cones. You measure from when the breaks are applied using data logging and telemetry...

Matt

 

Those formulas and estimates are worthless. OK So drop 300 lbs from the car (rip out some interior). By your 'estimates' now the car is 2-3 seconds quicker.

NOPE.

The only FACT is, there is no real data showing how much of a difference this makes in the real world. People can argue butt-dyno formulas and throw around weights, times and percentages all day long. Point is no one knows.

It's my OPINION that this will have a very minor impact, probably one that equates to less than a car length 0-60, and the same braking. It's my OPINION that it would be more obvious to the auto-x'r but still not a day and night difference. It is my OPINION that changing the runflats to performance tires has more of an effect on handling and perception due to the composition and design of the tread more so than simply the weight difference.

 

there is no mystery here. The errors in my calculation had to do with not accounting for the rotating mass accuratly, and not integrating the benefit through the whole acceleration curve. This is science, not magic! You release chemical energy, and convert it to kinetic energy. That's it. This enegy goes into moving the car, spinning parts, moving air, and some heat.

So keep to your opinions, and I'll stay with conservation of energy and momentum, along with F=Ma, and some thermodynamics.

So stay with your opinion, that fine with me. But if you think estimates like mine are useless, it appears you don't understand the value of approximations, or engineering. If the moment of inertia for tires and wheels were posted like the mass, this would just be a question for a high school physics class.

one other point, small deviations can be handled with linear approximations. If you want to get nerdy about this, this is the basis of Taylor series expansions, as well as perterbation theory. But if the deviation is large, then you have to do the non-linear math, and to this I will admit every day.

So you say it's your opinion that it's less than a car length. I gave some math, with an expanation of the assumptions, and come to a conclusion that is in line with some data posted here. And you didn't comment on any one of them! that's just being ornary.

Matt

 

Well, If I remember correctly, 1/10 of a second equals about one car length. So that sounds about right.

Oh, and I agree with Doc because he uses science to prove his position.

 

I did the math, and the only thing I didn't have for an acutal calculations was the additional rotational mass of the the other rotating parts. I'll add the link when I've finished the post.

Matt

Here it is....

https://www.northamericanmotoring.co...008#post527008

 

EDIT - I read your new thread and I agree! Your numbers line up with my estimates perfectly.

 

Oh and thank you for admitting your original post was wrong.

 

I'm not going to get into details, but there were other factors, which I can't remember if I posted. The difference was there, I could feel it. But don't trust me, do the testing yourself.
I'm not sure I'm experienced enough at launching the car...

Brian

 

I use racing tires on x lites for autox, and the run flats on s lites for daily driving. There is a BIG difference in the feel of the car with the lighter rims and tires. You can feel this in acceleration, braking, and how easy the car is to turn. I DO believe that "the butt dyno" tends to be a crock, but I wasn't expecting the difference to be that great. I figured the racing tires would help with cornering, but make no differenc otherwise. They do make a difference.

 

It is kind of frustrating that wheel & tire manufacturers don't ever list the main thing needed to estimate their effect on acceleration: the moment of inertia. If this were stated for any given wheel and tire (which by the way would be additive, so tires & wheels could be mixed & matched), it would be straight forward to figure out how much power would be consumed in spinning the wheel up to, say 60 mph. There must be a way, knowing the power consumption of the wheels, the speed - torque curve of the engine and weight of the car, to estimate how much any given wheel/tire package would affect acceleration (neglecting things like air resistance and road friction).

 

I'm trying the above reasons to talk my wife into letting me get some cool looking (and lighter) rims, but she knows why I really want some cool looking (and lighter) rims.
For those who don't believe lighter is better, try doing a Huffy Toss contest (mountain bikers throwing cheap bikes the greatest distance). What moves the most on any car? Hello?!

 

So, what is considered to be a lightweight wheel which is suitable for everyday street use (potholes, etc.) that is not more prone to breakage than an S Lite? I assume that, being heavy, the S Lite is a very strong wheel that is less likely to break; is that true?